He opened with hard-swinging contemporary jazz executed by a deft, astonishingly young-looking band.

Then Harrison brought on venerable Dr. Lonnie Smith -- born in 1942, he was Downbeat magazine's "Top Organist of 1969" and is still a renowned master of the Hammond B3 -- for some delightfully weird organ sounds.

Then Harrison put down his saxophone and reappeared in full Mardi Gras Indian finery for a pounding mini-set of street-parade music and chanting.

"I travel through so many different styles of music, it's all part of me," Harrison said in a recent interview. "My friend once said, 'You're a one-man jazz festival.' That's what lives in my heart. It sort of helps me to be able to mix genres, especially when I'm playing jazz."

Expect similar depth and breadth from Harrison when he takes to the Congo Square "My Louisiana" stage today at 1:15 p.m. at the New Orleans Jazz and Heritage Festival Presented by Shell.

Jazz Fest attendees who find their way to his set will also see a formative influence on "Treme," the new HBO drama.

Pieces of two principal characters in the show are drawn from Harrison's life.

The son of Guardians of the Flame Big Chief Donald Harrison Sr., Harrison has made his way in the wider world of jazz beyond New Orleans much like Delmond Lambreaux has in the series. (That was Harrison on the bandstand with Lambreaux in the New York nightclub scene in the series' premiere episode).

As Big Chief of the Congo Nation, Harrison is a committed keeper of the Mardi Gras Indian flame in New Orleans, deeply informing Delmond's father, bassist-carpenter-Indian chief Albert Lambreaux.

Part of a team of locals and consulting on or serving as muses for the series -- including musician/disc jockey Davis Rogan (the model for the Davis McAlary character) and chef Susan Spicer (part-inspiration for Janette Desautel) -- Harrison first met "Treme" co-creator David Simon when Simon was still making episodes of his Baltimore-set HBO series "The Wire."

After Hurricane Katrina, Simon placed New Orleans music on "The Wire" soundtrack, including a song by Harrison. The relationship developed from there.

"He was just observing and, I guess, making mental notes and seeing what I was doing and how I was doing it," Harrison said. "That's what it seemed like to me. We did sit down to lunch once, but it wasn't like a formal interview. We were just talking, a casual conversation. But maybe he was leading that casual conversation. He's quite a smart guy."

The one significant difference between Harrison's story and Delmond Lambreaux's is Harrison's comfort with the footsteps he literally walks in as a Mardi Gras Indian.

"I think he is very comfortable with the Indian tradition," Simon said. "He doesn't feel any conflict between his New York endeavors and his sense of being a New Orleanian.

"It was much more interesting to us (for the Delmond character) to feel that father-son dissonance that a lot of young men have growing up. You want to stand in your own light."

Added Harrison: "It's loosely based on how I came into being as a musician. During this stage in his development, he doesn't like New Orleans that much, which is something that is not part of my character. I've always loved New Orleans music. I know why they're doing it."

In his role as consultant for the series, Harrison has reviewed scripts and worked closely with actor Clarke Peters, whose amazing performance as Albert Lambreaux has arrested viewers' attention and appears a contender for an Emmy Award nomination.

"He's a great actor and a great person and he's a natural bass player, which was surprising to me," Harrison said. "He really understands the nature of the upright bass. I thought he'd been playing for years, and he told me he's only been playing since the series started, which kind of blew my mind. He really understands what that instrument's supposed to do."

Harrison said Peters has worked hard to capture an Indian chief's almost-aristocratic mien.

"I think what the series has picked up on is the seriousness that people who do that have," Harrison said. "They maintain the culture and the spirituality of it, and the transcendence from everyday life. Those are some of the things I think Clarke really brings out. And the regal nature of being a big chief."

Peters credited Harrison with letting him in on elements of the Indian culture that only an insider could know.

"I've gleaned that there's this tradition going on, and the remnants of it may not be in people's intellect, but it's in their hearts, it's in their dance moves," Peters said. "You have to be here to really understand what it is. It might look wonderful and eccentric and fun, but there are layers that are a lot more profound than just what we derive."

Peters added he's also learned a lot of very specific choreography and attitude from Harrison.

"I've gotten a lot of moves from Donald," Peters said. " 'Hold your head up, you're a chief.' 'Don't put your spear on the ground, because that means war.'

"I say, 'But it's just a stick,' and he says, 'Don't you dare think that's just a stick.'

"Donald's been really, really helpful."

Added Simon: "It's not easy on the consultants. There are moments that character has that are unlike what he knows to be indicative of his late father and other chiefs. He has to sort of hold his breath and go, 'This is fictional. This didn't happen.' But at the same time, (the consultants) provided us with a lot of interior logic in order to create the characters."

Harrison sees "Treme" as an opportunity to educate the world beyond New Orleans about underappreciated elements of its culture. He also believes that "Treme" could play a role in helping preserve that culture.

"What the show is doing for me is letting the world know that something is going on down here in New Orleans, and it's one of the root cultures and music styles that have influenced the whole world from the beginning," he said. "I think it's important to let the world know that we can't throw this culture away.

"A tree without roots is not going to survive. This is a strong foundation that much of our art and culture is based upon -- not just New Orleans, but the world. This is what we feed off of."